Saturday, September 25, 2010

Story first, statistics later

I stumbled across this little gem of a Slate article about the FDA’s bizzare “Drug Drop-off Day”. In it, the author goes after the NYTimes for using bizarrely bogus statistics to support the premise that the abuse of prescription opiates is leading to an increase in motor vehicle deaths. When you dive in, the Times first pulls a bait-and-switch by including both prescription and illegal drugs, and then fails to consider that the percentage may be getting larger because the denominator (all motor vehicle deaths) is getting smaller (which it is; quite drastically), instead of the numerator getting larger (more DWI).

Percentages are slippery things – they can be used to show a trend where there isn’t one, with careful choice of denominator and numerator. My friend Elmo Iscariot responded to my Tale of Two Countries with a post that included an interesting comment about how New Jersey has the most privately-owned guns per square mile. At the same time, when I go poking around, New Jersey has one of the smallest (behind MA and tied with HI) percentage of gun owners in the country.How can both be true? Well, there’s a third factor; New Jersey is the most densely-populated state in the Union, and the last time I checked, had the most densely populated location in the world as of a couple years back. A small percentage can still have a large absolute value when the denominator is large enough. This would go a long way towards explaining why, even in New Jersey, I have within an hour’s drive of my house, well over 60 ranges, gun stores, &c; with a good half-dozen of the ranges open to the public. Just as an illustration, I had gone down to the Northern VA region for the 4th of July weekend with the intention of shooting at the NRA’s newly-refurbished facility in Fairfax City, VA as one of my activities. Once I got there, I found out that the refurb work was not yet complete, and the range would be closed that Monday still. I poked around looking for a backup plan, and was unable to find one that was clearly open to the public; at least not where I could shoot pistol (which is what I had at the time).

This isn’t news, either. After all, the quote “Lies, damned lies, and statistics” was popularized by Mark Twain and attributed to various Victorian politicians. It’s more honest to find the figures, then write the story. It’s more effective to writ ethe story, then find the figures, though.

1 comment:

  1. Yup. High population densities make for large absolute numbers at the ends of the bell curve. It's why there are so many gun owners in New Jersey and why, reportedly, there have always been a heck of a lot of peaceful Chicago citizens who carried guns: it takes a very dedicated person to defy layers and layers of abusive laws and officials in the name of self defense, but in a city of almost three million, you'll get plenty of those dedicated outliers.


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